The present invention relates to a device for detecting the manner in which a vehicle seat is occupied, a stereoscopic image recording device having at least one optical sensor recording the scene at the vehicle seat, and deriving from that a three-dimensional map partitioned into a plurality of zones, giving, for each zone, the distance from a reference point.
Investigations, e.g. by NHTBA (National Highway Traffic Safety Administration) have shown that children, sitting in the passenger seat of the vehicle, in particular in a backward aligned child""s seat, have suffered deadly injuries from the realease of an airbag. A releasing airbag, in general, poses a danger of injury to a person in the vehicle seat, when this person, for reasons of sitting position, body size or leaning forward in the direction of the airbag prior to the occurrence of the accident, is at too short a distance from the airbag. There are occupational situations, especially in the case of the passenger seat, in which the airbag should better not be released. Among such occupational situations belongs, for example, the occupation of the vehicle seat by a child""s seat, or laying down articles not needing protection, or a much too small clearance between the passenger and the airbag. Intelligent airbag systems for use in the future should be in a position to match the amount of airbag inflation to the size and the sitting position of the current vehicle occupant.
That certainly shows that it is unavoidable, for the control of the airbag""s release, to detect the manner of occupation of the vehicle seat, in order to avoid unnecessary release of the airbag, or endangering the person in the vehicle seat. There already are different kinds of devices for recognizing the manner of occupation of the seat. A device for detecting the manner of occupation of a vehicle seat, described in the introduction, which has a stereoscopic image recording system, is described in German Patent No. 197 41 393. With the use of such a stereoscopic image recording device, distances of the vehicle seat area, divided by zones, form a reference point which can be ascertained with the aid of the known triangulation method. A so-called three-dimensional map containing a plurality of zones is generated thereby, from which can be read with great accuracy whether and how the vehicle seat is occupied, or which sitting position a vehicle passenger sitting on it has assumed for the moment. This information can now be used for controlling restraint systems such as airbags or belt tighteners.
The accuracy of a three-dimensional map created by a image recording device depends strongly on the image-taking quality of the optical sensors. The scenic lighting conditions have a strong influence on the image quality. In motor vehicles, especially, very extreme lighting conditions come about. This is true for one, because the motor vehicle is in an open environment. That means that the most varied lighting conditions are possiblexe2x80x94day, night, low-in-the-sky and blinding sun, blinding headlights of other vehicles, etc. Besides that, a vehicle can move very fast, so that lighting conditions can change a great deal in a short space of time (e.g. while driving into a shaded region, while leaving a tunnel and the like. Linear optical sensors, as are used for the recognition of seat occupation according to German Patent No. 197 41 393, show a very great dependence on changes in brightness of the recorded scene. In order to reduce as far as possible the great brightness dynamics occurring in the vehicle, a strong light source for lighting the scene being looked at is required, according to German Patent No. 197 41 393.
The present invention now is based on the object of presenting a device, of the kind mentioned at the beginning, which, in spite of the great brightness dynamic, and even without using a very strong light source, can reliably identify the kind of occupation of a vehicle seat.
The object mentioned is attained, in that the at least one optical sensor, which is contained in the stereoscopic image recording device, has a nonlinear transformer characteristic describing the correlation between the entering light intensity and its electrical output, whose characteristic curve steepness decreases with increasing light intensity. Such a nonlinear optical sensor is capable of recording the scene at the vehicle seat with high resolution, even during great brightness dynamics, only a low-cost light source being required for illuminating the scene.
Optical sensors whose transducer characteristics have a logarithmic pattern are particularly suitable for recording scenes with very great brightness dynamics.
For the realization of a stereoscopic image recording device, either optical sensors arranged at defined distances from one another can be provided, or a stereooptical instrument, which images two images of the vehicle seat, offset to each other by a defined amount, on a single optical sensor.
Preferably, a light source is available for illuminating the scene of the vehicle seat, which shines synchronously with the activation of the image recording device. It is expedient if the light-source shines a light in the infrared region, invisible to the vehicle passengers. In order to keep disturbing scattered light away from the image recording device, an infrared band-pass filter is preferably arranged immediately in front of the at least one optical sensor, whose range lies within the light-sensitive range of the optical sensor.